1. Field of the Invention
This invention relates to improved torsional characteristics of metals and a process and apparatus for strengthening metals, and more particularly, relates to metal wire with superior torsional yield strength, and a process and an apparatus for increasing the torsional yield strength characteristic of metals.
2. Background of the Invention
Twisting of wires to form a cable is well known in the wire drawing art; drawing a plurality of twisted wires through a die is also well known. In U.S. Pat. No. 2,250,610, it has been suggested to draw a single wire through a die or series of dies while twisting the wire and causing a back tension thereon. In addition, increase in corrosion resistance in stainless steel spring material is taught in British Pat. No. 722,427; precipitation of carbides in stainless steel is taught in U.S. Pat. No. 2,549,468; a method of increasing the tensile strength of a special type of 18-8 stainless steel is taught in U.S. Pat. No. 2,795,519 and an article entitled "High-Strength Stainless Wire And Strip Made of Iron -- Chromium -- Nickel -- Based Alloys" by M. N. Reavskaya in the magazine "Steel in the U.S.S.R."; a method of heat treating a modified 5% chromium tool steel is discussed on pages 420-428 in the 1962 TRANSACTIONS OF THE ASM; and special dies, rollers, and devices for changing the strength characteristics of metals are taught in U.S. Pat. Nos. 300,741; 1,525,730; 1,749,671; 1,967,487; 367,733; 3,038,592 and 3,158,258. In fact, many different proposals have been presented, including the ones mentioned above, to mechanically work metal strips or wires in order to increase tensile strength thereof. However, the torque transmitting ability (torsional strength) of metal wire, such as required in springs, is of great significance and greater increase in torsional strength of wires used for such products is highly desirable but not recognized or satisfactorily achieved by this prior art.